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      1 /*
      2  * Copyright 2013 Google Inc.
      3  *
      4  * Use of this source code is governed by a BSD-style license that can be
      5  * found in the LICENSE file.
      6  */
      7 
      8 #ifndef SkMessageBus_DEFINED
      9 #define SkMessageBus_DEFINED
     10 
     11 #include "SkLazyPtr.h"
     12 #include "SkTDArray.h"
     13 #include "SkThread.h"
     14 #include "SkTypes.h"
     15 
     16 template <typename Message>
     17 class SkMessageBus : SkNoncopyable {
     18 public:
     19     // Post a message to be received by all Inboxes for this Message type.  Threadsafe.
     20     static void Post(const Message& m);
     21 
     22     class Inbox {
     23     public:
     24         Inbox();
     25         ~Inbox();
     26 
     27         // Overwrite out with all the messages we've received since the last call.  Threadsafe.
     28         void poll(SkTDArray<Message>* out);
     29 
     30     private:
     31         SkTDArray<Message> fMessages;
     32         SkMutex            fMessagesMutex;
     33 
     34         friend class SkMessageBus;
     35         void receive(const Message& m);  // SkMessageBus is a friend only to call this.
     36     };
     37 
     38 private:
     39     SkMessageBus();
     40     static SkMessageBus* Get();
     41     static SkMessageBus* New();
     42 
     43     SkTDArray<Inbox*> fInboxes;
     44     SkMutex           fInboxesMutex;
     45 };
     46 
     47 // This must go in a single .cpp file, not some .h, or we risk creating more than one global
     48 // SkMessageBus per type when using shared libraries.
     49 #define DECLARE_SKMESSAGEBUS_MESSAGE(Message)                        \
     50     template <>                                                      \
     51     SkMessageBus<Message>* SkMessageBus<Message>::Get() {            \
     52         SK_DECLARE_STATIC_LAZY_PTR(SkMessageBus<Message>, bus, New); \
     53         return bus.get();                                            \
     54     }
     55 
     56 //   ----------------------- Implementation of SkMessageBus::Inbox -----------------------
     57 
     58 template<typename Message>
     59 SkMessageBus<Message>::Inbox::Inbox() {
     60     // Register ourselves with the corresponding message bus.
     61     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
     62     SkAutoMutexAcquire lock(bus->fInboxesMutex);
     63     bus->fInboxes.push(this);
     64 }
     65 
     66 template<typename Message>
     67 SkMessageBus<Message>::Inbox::~Inbox() {
     68     // Remove ourselves from the corresponding message bus.
     69     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
     70     SkAutoMutexAcquire lock(bus->fInboxesMutex);
     71     // This is a cheaper fInboxes.remove(fInboxes.find(this)) when order doesn't matter.
     72     for (int i = 0; i < bus->fInboxes.count(); i++) {
     73         if (this == bus->fInboxes[i]) {
     74             bus->fInboxes.removeShuffle(i);
     75             break;
     76         }
     77     }
     78 }
     79 
     80 template<typename Message>
     81 void SkMessageBus<Message>::Inbox::receive(const Message& m) {
     82     SkAutoMutexAcquire lock(fMessagesMutex);
     83     fMessages.push(m);
     84 }
     85 
     86 template<typename Message>
     87 void SkMessageBus<Message>::Inbox::poll(SkTDArray<Message>* messages) {
     88     SkASSERT(messages);
     89     messages->reset();
     90     SkAutoMutexAcquire lock(fMessagesMutex);
     91     messages->swap(fMessages);
     92 }
     93 
     94 //   ----------------------- Implementation of SkMessageBus -----------------------
     95 
     96 template <typename Message>
     97 SkMessageBus<Message>::SkMessageBus() {}
     98 
     99 template <typename Message>
    100 /*static*/ SkMessageBus<Message>* SkMessageBus<Message>::New() {
    101     return SkNEW(SkMessageBus<Message>);
    102 }
    103 
    104 template <typename Message>
    105 /*static*/ void SkMessageBus<Message>::Post(const Message& m) {
    106     SkMessageBus<Message>* bus = SkMessageBus<Message>::Get();
    107     SkAutoMutexAcquire lock(bus->fInboxesMutex);
    108     for (int i = 0; i < bus->fInboxes.count(); i++) {
    109         bus->fInboxes[i]->receive(m);
    110     }
    111 }
    112 
    113 #endif  // SkMessageBus_DEFINED
    114